Calcium phosphate scale formation from simulated milk ultrafiltrate solutions

Calcium phosphate deposit formation caused by the flow of SMUF (simulated milk ultrafiltrate) solutions was studied under well-defined hydrodynamic conditions at 60 and 70degreesC in the pH range 5.8-7.0. At 60degreesC maximum deposit formation of mostly amorphous calcium phosphate occurs in the pH range of 6.2-6.4, and at a somewhat lower pH at 70degreesC. Above pH similar to6.3 bulk precipitation occurs, depleting the solution of scale-forming ions and resulting in reduced deposition rates. At the maximum deposition rate, an initially thin and well-adhering layer is formed, entirely covering the substrate within minutes from the onset of flow. Further growth occurs mostly in the form of overgrowths consisting of clusters of submicron particles. By employing two different pipe diameters, a range of Reynolds numbers from 7000 to 17,000 was covered. With increasing flow velocity the deposition rate tends to increase, while more compact deposit layers are obtained. Preliminary experiments provide no clear evidence that the deposited mass is affected by the surface treatment or the type of substrate material; however, reduced adhesion to the modified surfaces is likely.